Catalyst for regulating the molecular weight distribution of ethylene polymers

Abstract

A vanadium-based catalyst is treated with certain silicon-containing compounds as a means of narrowing and effectively regulating the molecular weight distribution of the polymers produced with the catalyst.

We claim: 
     
       1. A solid catalyst precursor consisting of: (1) a solid, particulate, porous, inorganic carrier, as support for   (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor,   (3) a boron halide or alkylaluminum modifier, and   (4) a silicon containing molecular weight distribution regulator having the formula   (RO).sub.n SiR.sup.1.sub.(4-n)        wherein: R is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms,   R 1  is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms, and     n is an integer having a value of from 1 to 4.   
     
     
       2. A solid catalyst precursor as in claim 1 wherein R and R 1  are alkyl radicals containing from 1 to 6 carbon atoms or aryl radicals containing 6 carbon atoms. 
     
     
       3. A solid catalyst precursor as in claim 2 wherein the silicon containing molecular weight distribution regulator is tetraethoxysilane. 
     
     
       4. A solid catalyst precursor as in claim 2 wherein the silicon-containing molecular weight distribution regulator is diethyldiethoxysilane. 
     
     
       5. A solid catalyst precursor as in claim 2 wherein the silicon-containing molecular weight distribution regulator is diisobutyldimethoxysilane. 
     
     
       6. A solid catalyst precursor as in claim 2 wherein the silicon containing molecular weight distribution regulator is diphenyldimethoxysilane. 
     
     
       7. A catalyst system comprising: (A) the solid catalyst precursor of claim 1,   (B) an alkylaluminum cocatalyst having the formula   Al(R.sup.3).sub.3        wherein: R 3  is a saturated hydrocarbon radical containing from 1 to 14 carbon atoms, and     (C) a halohydrocarbon polymerization promoter having the formula   (R.sup.4).sub.b CX'.sub.(4-b)        wherein: R 4  is hydrogen or an unsubstituted or halosubstituted alkyl radical containing from 1 to 6 carbon atoms,   X' is halogen, and   b is 0, 1 or 2.     
     
     
       8. A catalyst system as in claim 7 wherein R and R 1  are alkyl radicals containing from 1 to 6 carbon atoms or aryl radicals containing 6 carbon atoms. 
     
     
       9. A catalyst system as in claim 8 wherein the silicon containing molecular weight distribution regulator is tetraethoxysilane. 
     
     
       10. A catalyst system as in claim 8 wherein the silicon-containing molecular weight distribution regulator is diethyldiethoxysilane. 
     
     
       11. A catalyst system as in claim 8 wherein the silicon containing molecular weight distribution regulator is diisobutyldimethoxysilane. 
     
     
       12. A catalyst system as in claim 8 wherein the silicon containing molecular weight distribution regulator is diphenyldimethoxysilane. 
     
     
       13. In a catalyst system comprising (A) a solid catalyst precursor consisting of (1) a solid, particulate, porous, inorganic carrier, as support for   (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and   (3) a boron halide or alkylaluminum modifier,     (B) an alkylaluminum cocatalyst, and   (C) a halohydrocarbon polymerization promoter, the improvement wherein the solid catalyst precursor (A) is treated with a silicon containing molecular weight distribution regulator having the formula     (RO).sub.n SiR.sup.1.sub.(4-n)     wherein:     R is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms,   R 1  is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms, and   n is an integer having a value of from 1 to 4.   
     
     
       14. A catalyst system as in claim 13 wherein R and R 1  are alkyl radicals containing from 1 to 6 carbon atoms or aryl radicals containing 6 carbon atoms. 
     
     
       15. A catalyst system as in claim 14 wherein the silicon containing molecular weight distribution regulator is tetraethoxysilane. 
     
     
       16. A catalyst system as in claim 14 wherein the silicon containing molecular weight distribution regulator is diethyldiethoxysilane. 
     
     
       17. A catalyst system as in claim 14 wherein the silicon-containing molecular weight distribution regulator is diisobutyldimethoxysilane. 
     
     
       18. A catalyst system as in claim 14 wherein the silicon-containing molecular weight distribution regulator is diphenyldimethoxysilane.